1. Field of the Invention
The present device relates to surface wear measurement and is used in the machinery industry. More specifically, the device is intended for an evaluation of working surface fretting wear characteristics.
The surface wear depends on the properties of interacting surfaces and applied loads. Fretting wear is a mechanical wear of surfaces in contact relative to each other in response to small vibratory movements thereof. Those micro movements, depending on the type of interaction, can take place in various directions. An example of that is the mating of a case bearing hole and the outer surface of the bearing cup where radial movements of the bearing cup relative to hole surface are caused by the system eccentricity. The offset value and the character of the movement are subject to the mating pressing force. Because of the axial eccentricity, axial (i.e. along the axis) movements of the bearing cup relative to the hole surface arise. Additionally, the surfaces in contact can move due to bearing ring spinning relative to the hole surface. Under real-life conditions, the micro movements of the surfaces as a result of spinning and axial eccentricity predominantly take place. Also, the surface machine direction and inner structure orientation work upon the intensity of fretting wear. All this means that the ability of a device to examine fretting wear through the micro movements in all the directions and the influence thereof becomes an important advantage of such device.
2. Description of the Related Art
Various methods and devices are known to evaluate wear. A device for testing fretting wear of ball-bearings is disclosed in the U.S. Pat. No. 6,715,336 of Apr. 6, 2004. In the patent, the working surface is treated by pressing a sphere to a plane (Z-direction) by two piezo actuators and moving it horizontally (X-direction). The loads are provided accurately, though only in two directions, therefore it is not possible to evaluate a potential displacement of the surfaces in the third axis (Y) direction.
The Chinese application CN 103 604 713A of Feb. 26, 2014 discloses a friction pair composed of two samples, a flat and a cylindrical (a tube) ones, contacting along a line. The cylindrical sample rests on two other cylindrical samples. The flat sample is attached to a vertical cylindrical rod which is adapted to vibrate in a vertical direction by means of a piezo element. In this way, a multidirectional radial-tangential movement is said to arise. The disclosure shows an uncontrolled and unregulated movement of the contacting surfaces relative each other in two directions (Z and either X or Y).
Known from the Japanese application JP 2005 249462A of Sep. 15, 2005 is a device for a biaxial movement to model fretting wear along X (or Y) and Z axes. In the device, a sphere is pressed to a holder by a piezo actuator and vibrated in the Z-direction, whereas the holder is vibrated in the X-direction on the horizontal plane by another piezo actuator. The device is believed to be the closest analogue (prototype) to the present device. Since there is provided a single piezo element for X and Y, movements along those axes are not independent.
The prototype does not seem to provide the possibility to evaluate the fretting wear through the surface displacement in the third (Y) axis direction, as well as to observe the surface wear continuously during the test. To rectify this disadvantage, a cardinal restructuring the device would be needed, including a reconstruction of a system of fixation of the holder.
Since fretting wear of the surfaces of materials usually takes place in response to simultaneous micro displacement of surfaces in all three directions (X, Y, Z), a need exists for a device capable of the fretting wear characteristics evaluation where three-directional controlled and regulated micro movements of the surfaces relative to each other are provided.